Accuracy of a first diagnosis of asthma in primary health care.

BACKGROUND: In a postal questionnaire study, the prevalence of asthma in southern Sweden has been found to be 5.5%. However, the register prevalence of asthma obtained from the medical records in the same municipality and age groups was found to be only 2.1%. OBJECTIVES: The aims of the study were to investigate whether the low register prevalence of asthma was caused by an underdiagnosis of asthma in primary health care and to validate a first diagnosis of asthma set by GPs in primary health care. METHODS: During a period of 3 months in 1997, all patients seeking care in the primary health care units of the municipality of Lund (population 171 877) with upper or lower airway infections, prolonged cough, allergic rhinitis, fatigue or a first positive diagnosis of asthma were recorded ( n = 3025). RESULTS: In the whole group of 3025 patients, 99 patients were found to have received a diagnosis of asthma for the first time during the study period. The diagnosis was verified in 52 of those 68 patients who attended a follow-up and examination by a respiratory physician. Among the remaining 2926 patients, 221 patients were selected randomly to constitute a control group. In this group, three patients were found to have asthma. Thus, the specificity of an asthma diagnosis set in primary health care was 0.99 [95% confidence interval (CI) 0.99-1.00] and the sensitivity was 0.59 (95% CI 0.31-0.81). CONCLUSIONS: The GPs in this study were good at excluding those who did not have asthma (specificity 99%) but less good in correctly diagnosing those who actually had current asthma (sensitivity 59%), which suggests an underdiagnosis of asthma